1. Field of the Invention
This invention relates to an aluminum nitride sintered body having a relatively small temperature dependence of volume resistivity as well as an electronic functional material or an electrostatic chuck employing the same, respectively.
2. Description of Related Art
At present, an electrostatic chuck is used for attracting and holding a semiconductor wafer in film forming processes for the semiconductor wafer such as transportation, light exposure, chemical vapor deposition (CVD), sputtering and the like, or steps of micromachining, cleaning, etching, dicing and the like. As a substrate for the electrostatic chuck, dense ceramics have been used. Particularly, a halogenous corrosive gas such as CIF.sub.3 or the like is frequently used as an etching gas or a cleaning gas in an apparatus for the manufacture of the semiconductor. A dense aluminum nitride has a high corrosion resistance against the above halogenous corrosive gas. And the aluminum nitride is also known to be a high thermal conductive material and to be high in the thermal shock resistance. Therefore, it is considered that it is preferable to make the substrate of the electrostatic chuck for the semiconductor manufacturing apparatus from an aluminum nitride sintered body.
In general, when the aluminum nitride is used as a substrate material for the electrostatic chuck, it is preferable that a volume resistivity is within a range of 10.sup.8 -10.sup.13 .OMEGA..multidot.cm at operating temperatures. However, the volume resistivity of aluminum nitride extremely decreases, for example, from 10.sup.16 .OMEGA..multidot.cm to not more than 10.sup.7 .OMEGA..multidot.cm over a range of room temperature to 600.degree. C., so that it is impossible to develop the stable operation as the electrostatic chuck in such a wide temperature range. Therefore, a service temperature of the electrostatic chuck is limited to a range of, for example, 200-400.degree. C.